Selections is a simple GTK+ app that copies whatever is in the PRIMARY selection. It builds a list of strings you've selected; you can then select an item and paste elsewhere. Useful if you want to collect a bunch of urls (or words, or whatever) and look them up later.
A screenshot is here. [800x600, 66KB]
Needs gmake and GTK+ 1.2.8 (or higher) to build.